1. Field of the Invention
The present invention relates to a method of grinding the back side of a wafer to improve the die strength of the wafer.
2. Description of the Related Art
The back side of a wafer having a plurality of devices such as ICs and LSIs on the front side is ground to reduce the thickness of the wafer to a predetermined value. Thereafter, the wafer is separated into the individual devices, which are in turn used in various kinds of electronic equipment. In recent years, the thickness of the wafer in the condition prior to separation into the individual devices has been further reduced to meet the requirement of further reduction in size and weight of electronic equipment. In the case that the back side of a wafer is polished to reduce the thickness of the wafer to 100 μm or less, for example, there arises a problem such that a gettering effect of suppressing the motion of heavy metal such as copper contained in the wafer may be reduced to cause a reduction in quality of each device separated from the wafer.
To cope with this problem, there has been proposed a technique such that the back side of a wafer is ground to form a strain layer, thereby producing a gettering effect and accordingly suppressing the motion of heavy metal in the wafer (see Japanese Patent Laid-open No. 2006-41258, for example). However, in the case that the strain layer is formed on the back side of the wafer, the die strength or strength against fracture of each device separated from the wafer may be reduced to cause a reduction in quality and life.